(1) Field of the Invention
This invention relates in general to methods and means for producing liquid droplets bearing electrical charges; more particularly, to methods and means for electrical charging of large volumes of liquid, and for producing electrically-charged droplets of liquids flowing at rates in the order of many gallons per minute per spray nozzle, over a wide range of electrical conductivity of liquid.
(2) Description of the Prior Art
The use and application of charged liquid droplets is well known, for example, in electrostatic spray painting, air pollution control, and spraying of pesticides. There could be substantially greater and more widespread use and application of electrically charged liquid droplets but for the fact that all existing droplet charging systems, as known to the applicants, have extremely small liquid flow rates, at most typically less than a few tenths of a gallon per minute per spray nozzle. Thus, up to now, electrostatic induction of charges on a surface of water, for example, has been limited to water flowing at small volume rates because it is necessary to maximize the ratio of liquid surface area to liquid volume. To charge water efficiently, spray nozzles comprising essentially capillary tubing, or orifices less than 20 mils in diameter, are used to eject water streams through or near non-contacting charging electrodes for the purpose of inducing electrical charge on the surfaces of these water streams. Droplets of water are formed in a region of the fine water stream after leaving the nozzle structure, and in the most efficient prior art nozzle designs the charging electrode extends beyond the region in which the charge is formed on the liquid surface, so as to preserve the charge on the droplets. The region of droplet formation can begin either immediately upon leaving the nozzle or at a distance therefrom, depending upon the particular nozzle design. The result is a high level of electrostatic charge per unit volume of the resulting water droplets, but the volume per unit time per nozzle is very small. Any attempt to increase the volume of liquid flow, as by increasing the diameter of the water discharge, lowers the ratio of liquid surface area to liquid volume resulting in a uselessly low level of electric charge per unit volume of liquid spray.
To our knowledge, all liquid charging systems up to the present time which are intended to charge large volumes of water, and to produce electrically-charged droplets of liquids flowing at large unit volume rates, have made use of a multiplicity of nozzles having fine, capillary-like spray orifices. These devices plug easily with suspended solids; they are complicated and expensive to fabricate; and they are difficult and expensive to maintain.